In all, about 4.7-million U.S. service members served during World War I. Last year, the U.S. Department of Veterans Affairs listed three known living WWI veterans: Landis; Frank Buckles, 107, of West Virginia; and J. Russell Coffey of Ohio.

Coffey, who was the oldest known American survivor, died in December at age 109.

Buckles is still alive, the VA said. He lied about his age to enlist at age 16.

VA spokesman Jim Benson said the agency tried to determine if there were other living WWI veterans.

"I think it's amazing for us to realize that you have this population of individuals who served during the first great war, and at that time, it was the war to end all wars," Benson said. "Soon, we will no longer have a living contact. It will all be from the histories left behind."